1. Field of the Invention
The present invention relates generally to the field of electrical wiring devices such as, by way of example, sensors, and more specifically to a control system using sensors to automatically control the flow of power to a load.
2. Description of the Related Art
Occupancy sensors are used for both security and/or to control room illumination by automatically turning the lights on when a room is occupied and off when the room is not occupied. Sensors are usually identified by the technology they use such as passive infrared sensors, active ultrasonic sensors such as Doppler shift detection sensors, audible sound detection sensors and microwave sensors. Sensors generally have two sections, a first section for sensing and a second section for load control. The sensing section can include detection and logic circuitry, and the section for load control can include a switching element. The switching element is normally used to connect line power to a load and disconnect line power from the load. It can also function as a switch for low voltage interface.
The various types of sensors mentioned above are further identified as being either low voltage sensors or self contained sensors. Low voltage sensors have separate sensing and load control sections where the low voltage sensor is packaged as a single product that is connected to a line voltage power pack having the switching element that is packaged in another product. Self contained sensors have the sensing section and load control section packaged as a single product. Low voltage sensors are generally used in commercial properties.
Self contained sensors are manufactured as either ceiling or wall mount sensors. Ceiling mount sensors are often used in commercial buildings. Wall mount sensors are more common and are produce in both commercial and residential versions. These sensors are often referred to as wall switch sensors or wall box sensors because they are designed to fit into a standard electrical box and can replace an existing wall switch. Wall switch sensors are powered by line voltage and have either a triac or mechanical relay which is used to disconnect line voltage from a load.
For retrofit installations in commercial buildings, it is generally not acceptable to require a neutral connection for the sensor to operate, because many existing buildings do not have a neutral wire in the wall box. The costs of rewiring the box with a neutral connection can be prohibitive and, therefore, most wall box sensors are powered by leakage current from line to ground. This leakage current is limited by code to no more than 500 uA. Sensors used in new construction require a neutral wire.
The use of sensors is increasingly being mandated by state building and energy codes. For example, California Title 24 requires the use of sensors in a specific number of rooms in a house. While sensors can be convenient for the automatic control of lights, they can be inconvenient when multiple points of control are needed. Existing sensors are not designed to accommodate remote control.
There are many situations in a home, especially in new construction, where there may be more than one point of control for lighting in a specific area or room such as a hallway, adjoining bathroom, kitchen, or where there is more than one entryway to the area. Traditional wiring methods using two 3-way mechanical switches, such as the Leviton 5603 switch, was designed for use where one load can be controlled from more than one location as shown in FIG. 1. The three way switch is a two position mechanical switch.
Multiple points of control is a common requirement of wall box dimmers. Dimmers have evolved over time to include this capability, generally in two ways. Dimmers can be divided into two types, electromechanical and digital. Electromechanical dimmers use a mechanical switch to turn the load on and off, and have a controllable semiconductor switch, such as a triac coupled in series to vary power to the load. These dimmers use a simple passive circuit to control the semiconductor switch. Digital dimmers also use a semiconductor switch, but generally use more complex logic, such as an ASIC or a microprocessor to control the switch. Digital dimmers usually do not have a mechanical switch. Instead, they rely on a smaller rated disconnect switch which is only used to provide an air gap for safety purposes.
The electromechanical dimmer can readily accommodate 3-way switching because it incorporates a true mechanical switch. Replacing the standard mechanical switch with a 3-way switch is all that is necessary and the electromechanical dimmer can be used with a standard 3-way switch to provide two points of control. Additionally, a 4-way switch can be used to provide up to 3 points of control. This, however, is the practical limit.
The digital dimmer cannot readily accommodate 3-way switching because it does not use a true electromechanical switch. However, the use of advanced logic, such as a microprocessor, allows a digital dimmer to overcome this limitation. A remote dimmer works well with a digital dimmer, and can provide remote control of the dimmer. The remote dimmer does not provide true 3-way switching, but does provide equivalent and additional functionality. For example, four or more remotes can be used to provide a total of five points of control for the digital dimmer.
A remote dimmer generally includes some switches and diodes and is connected to the dimmer with an additional “traveler” wire, similar to how a 3-way switch is connected to an electromechanical dimmer. It does not do any actual dimming, but acts as a source of information to the dimmer. The remote dimmer sends line voltage pulses to the dimmer which has a microprocessor pin which decodes these signals to indicate both the on/off or dim level and functions.
A digital dimmer provides a display which indicates the state of the load. Traditional remote dimmers have no display. Therefore, a user cannot identify the state of the load or the dim level by looking at a remote dimmer. An additional drawback is that the look of the remote is different than the look of the dimmer because there is no display in the remote dimmer.
To overcome these limitations, advanced remote dimmers have been developed that provide identical display and resembles a dimmer. This is performed by the innovative use of communication between the dimmer and the remote. See U.S. patent application Ser. No. 11/149,365, which is incorporated herein, in its entirety by reference for a disclosure of this technology and of an advanced remote dimmer, a simple remote dimmer and a switch. The advanced remote dimmer, such as that disclosed in U.S. patent application Ser. No. 11/149,365 has the advantage of allowing the use of both simple and advanced remotes together with the same dimmer at the same time. Prior art remote dimmer systems only allow the use of the simple remote dimmer or the advanced remote dimmer. In addition, the system disclosed in U.S. patent application Ser. No. 11/149,365 includes electronic switches which provide on/off control of non-dim loads, as well as the ability to work with both types of remotes, thus exceeding the multiple location control ability of the standard 3-way mechanical switches. The system includes switching remotes (which provides only an on/off control in the user interface) to work with (and match) the electronic switches.
In locations where sensors are required, it is still desirable to have multiple location control, but the design of traditional sensors cannot accommodate this. In addition, many homeowners want to be able to dim the lights at the same locations where the sensors are located. Again, this is not possible with the design of traditional dimmers and occupancy sensors.
When using occupancy sensors to control the lights in an area, it is possible that a single sensor's field of view is not enough to cover the entire area. In this case, it would by desirable to have additional sensors connected together to cover the desired area.